1. Field of the Invention
The present invention is directed to a process and apparatus for making powder rubber from recycled used rubber sources. More specifically, the present invention is directed to a process and apparatus for making powder rubber from a preprocessed source of used rubber particles having different average particle size ranges.
2. Background of the Prior Art
It is long been known that the disposal of used tires and other rubber articles represents a major environmental problem insofar as used tires overwhelm waste disposal sites and indiscriminate discarding of tires and like rubber articles create major environmental problems. It is for this reason that processes have been developed to dispose of tires in a manner that not only eliminates them as an environmental problem but provides incentives for practice of those tire disposal processes.
Early processes focused upon tire comminution which recovered the inherent fuel value of the significant combustible content of vehicle tires. More recently, processes which recover the rubber constituent of vehicle tires, for reuse in the manufacture of rubber-containing articles, have been developed.
Although these processes have encouraged environmental protection by providing processes for the utility of rubber in the further manufacturing of new rubber products, a major concern associated with these processes has been the inability to provide purchasers of the rubber products produced by these processes with a rubber material that can be readily incorporated into the purchaser's production feed. That is, randomness of comminution variables and the types and condition of the used vehicle tire feed have produced random rubber products. Probably, the most undesirable result of this random production has been the unpredictable rubber product particle size distribution. That is, although a lively market exists for powder rubber this market has not yet been fully exploited due to difficulties in producing commercial quantities of powder rubber in the particle size ranges required by tire and other rubber product producers, the target purchasers of powder rubber products.
The inventors of the present application have addressed this concern with a new process and apparatus embodied in U.S. patent application Ser. No. 10/714,782 filed Nov. 17, 2003.
Other related prior art includes U.S. Pat. No. 5,588,600. The '600 patent describes a process and apparatus for low temperature comminution of tires in which cryogenic fluids, employed in embrittling used rubber particles so that comminution can effectively occur, are recycled. This process produces of a sufficiently small particle size desirable to tire and other rubber product manufacturers. However, even the process and apparatus of the '600 patent provides no assurance that the cryogenic comminuting device can accommodate all rubber particle size feedstocks to produce particles in the powder rubber size range.
Other disclosures of processes and apparatus for reducing rubber to fine particle size include U.S. Pat. Nos. 5,368,240 and 4,863,106.
The above-discussed processes and apparatus address conversion of used rubber products into crumb or powder rubber utilizing comminuting techniques, in combination with the use of cryogenic fluids. What has not particularly been addressed in the development of the above-mentioned technology is the production of powder rubber from used rubber sources in an energy efficient manner. This is particularly important in view of the recent dramatic increase in petroleum costs.
This is also a disguised environmental concern. The higher cost of energy makes the cost of recovering powder rubber significantly more expensive. Unless the price of powder rubber is cost effective, rubber product manufacturers, especially tire manufacturers, will elect to employ virgin rubber. Without this market, there is insufficient incentive to produce these products with the resultant environmental problem of disposing of the ever increasing quantity of used tires.